In order to control driving of an AC electric motor using a DC power source, a method of driving using an inverter has been adopted. Switching of the inverter is controlled by a driving circuit. PWM (Pulse Width Modulation) control and rectangular wave voltage control (also referred to as rectangular wave control), for example, have been known for inverter control.
Japanese Patent Laying-Open No. 2007-306699 (Patent Document 1) discloses a motor drive system allowing switching between the PWM control and the rectangular wave control. The motor drive system includes a control circuit that executes the following control. When a d-axis current before the control is switched to the rectangular wave control is smaller than a command value, the control circuit corrects phase of a control voltage vector such that the d-axis current comes closer to the corresponding command value. The control circuit executes the rectangular wave control based on the corrected phase of the control voltage vector. When modulation factor is higher than a prescribed value, the control circuit switches the inverter control mode from the PWM control to the rectangular wave control. On the other hand, if the modulation factor is not higher than the prescribed value and q-axis current reaches a corresponding command value, the control circuit switches the inverter control mode from the rectangular wave control to the PWM control.    Patent Document 1: Japanese Patent Laying-Open No. 2007-306699